Combustion engines of the abovementioned kind are known and they reduce the fuel consumption and exhaust emissions compared to other two-stroke crankcase scavenged internal combustion engines. Two-stroke crankcase scavenged internal combustion engines can be built with low weight and size, are comparably easy to start when cold due to good atomization of the fuel since the fuel and air is mixed in the crank case. Further, they are also comparably cheap to produce and reliable at rough working conditions.
Two stroke engines using direct injection can reach even lower fuel consumption, since direct injection allows more precise control over fuel metering and injection timing. However, engines using direct injection have other problems compared to crank case scavenged engines. The primary disadvantages of direct injection engines are complexity, cost, size and weight. Direct injection systems are more expensive to build because their components must be more rugged—they handle fuel at significantly higher pressures than indirect injection systems and the injectors themselves must be able to withstand the heat and pressure of combustion inside the cylinder. Further direct injection engines also require a separate oil tank and components associated to lubricate the engine, while a crankcase scavenged engine can be lubricated using a fuel which is mixed with oil. For the above mentioned reasons size, weight and building costs of direct injection engines tend to increase, which of course is a disadvantage, especially for hand held working tools. Direct injection engine's can also be difficult to start when cold. This is particularly true when less volatile fuel types, such as alcohol based fuels which has had an increase in popularity since they can be produced from renewable resources, are used to power the engine. When the engine is cold, the fuel tends to atomize less, resulting in difficult starts. Further direct injection engines usually are battery assisted at start up to be able to inject the fuel at sufficient pressure and ignite. Once the engine is running, the environment into which fuel is introduced is both hotter and more turbulent for better fuel/air mixing and, consequently, better combustion.